PANNA: New Evidence That Endocrine Disruptors Block Sperm Function

The link between male fertility and hormone disrupting chemicals is now more fully understood. A new study shows that adult sperm, when exposed to hormone disrupting chemicals (often called endocrine disruptors), mature too quickly and fail to reach and fertilize the egg. Dozens of pesticides are known or suspected endocrine disruptors. The list includes widely used carbamates such as aldicarb and carbaryl, common organophosphates (e.g., malathion and chlopyrifos), and persistent chlorinated pesticides such as endosulfan, lindane and DDT. Individuals face potential exposure to endocrine disrupting pesticides through food residues, home pesticide use, and soil, water and air contaminated by agricultural pesticide use.

The study, released in early July 2002 at Europe's annual human reproduction conference by scientists from King's College in London, provides the first direct evidence that endocrine disruptors affect sperm function. For many years, the debate over male fertility has focused on the effects of prenatal exposure to such compounds on development of testicles in infants and evidence of declining sperm counts worldwide.

In the past ten years, dozens of studies have linked endocrine disrupting chemicals to a number of reproductive and other health effects. The chemicals closely mimic naturally occurring hormones and can disrupt the functioning of hormone systems in humans and other animals at very low levels of exposure. Dr. Theo Colburn's research more than a decade ago linking reproductive failure in alligators with chemical exposure led researchers to further explore the reproductive and other effects of this class of chemicals.

Exposure to endocrine disrupting pesticides adds to an individual's ongoing exposure to dozens of other chemicals that also mimic hormones, from by-products of industrial production and incineration (dioxins and furans) to chemicals in widespread use in formulating products for everyday use. Phthalates, for example, are endocrine disrupting chemicals used as softening agents in many plastic products (including medical devices) and in beauty products such as deodorants, lotions and nail polish.

The 12 chemicals (nine pesticides) to be banned worldwide under the international Stockholm Convention on Persistent Organic Pollutants are all known or suspected endocrine disruptors. While most of these chemicals have been banned in industrialized countries for many years, low-level residues continue to be found in the U.S. food supply (See Nowhere to Hide: Persistent Toxic Chemicals in the U.S. Food Supply, PANNA & Commonweal, 2001 on the PANNA website: http://www.panna.org/resources/documents/nowhereToHideAvail.dv.html.)

In the sperm function study, researchers found that mouse sperm bathed in low levels of endocrine disrupting chemicals matured early, releasing the enzymes they need to penetrate the egg's jelly coat before making contact with the egg. Scientists note that human sperm is known to be even more sensitive than mouse sperm to female hormones such as estrogen. The lead researcher, Dr. Lynn Fraser, also notes that given the wide variety of endocrine disruptors present in the environment, it is quite possible that sperm face exposure to multiple endocrine disrupting chemicals, with possible synergistic effects.

This evidence of the direct effects of endocrine disruptors on sperm function adds a new dimension to the ongoing debate over the links between male fertility and chemical exposures.

Declining sperm counts became a focus of discussion in 1992, when a landmark study was released by Carlsen et al reporting a 40% decline in sperm count worldwide over the second half of the 20th century. The study initiated a decade's heated exchange within the scientific community over sperm count data, and spurred many follow up studies producing a range of conflicting results. There now appears to be agreement that there have been significant sperm count declines, with unexplained regional variations. There is no agreed explanation for the declines, and endocrine disruption is considered one of the possible contributing sources.

The other area of intensive research linking chemicals and male fertility focuses on the increasing rates of "cryptorchidism," or undescended testicles, which can result in infertility. Here the discussion is less controversial, as evidence from both animal studies and studies of children with cryptorchidism point toward a link with endocrine disrupting chemicals, and the process through which chemicals can block the hormonal signal controlling testicular descent is clearly understood.

The recent evidence on blocked sperm function adds new urgency to regulatory efforts to understand and address endocrine disruptors. The U.S. Environmental Protection Agency's Endocrine Disruptor Screening Program, established in 1996 under the Food Quality Protection Act to test pesticides and other chemicals for endocrine disrupting effects and prioritize them for regulatory action, has been unacceptably slow to identify and recommend action on priority chemicals.
Evidence of the health effects of endocrine disrupting chemicals continues to mount. In terms of male fertility, it now seems that these ubiquitous chemicals are a significant threat at various stages, from testicular development to sperm production to the functionality of healthy sperm. This class of chemicals appears to be threatening male fertility on several fronts.

"Effects of estradiol 17B and environmental estrogens on mammalian sperm function," Fraser L.R. et al, Presented at the annual conference of the European Society of Human Reproduction and Embryology, Vienna. July 2002 (http://conf.eshre.com/PDF/O-119.pdf).

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